Bitumen is a key ingredient for pavement, roofing and waterproofing applications. A primary use of bitumen is in pavement applications, such as road construction. At ambient temperature, bitumen is an essentially solid material, but at elevated temperatures, the bitumen is a flowing fluid. In e.g. road construction, a mixture of bituminous binder and aggregates, such a divided rock material, i.e. an asphalt composition, is laid down on a bedding to produce a wear resistant paving.
One common method of paving is commonly referred to as the hot-mix method, wherein heated bituminous binder is mixed with aggregates to produce a hot, flowing asphalt composition. The bituminous binder is heated to a temperature at which it is fluid enough to properly cover the aggregates. The aggregates are typically heated prior to the mixing with the bituminous binder, on the one hand to obtain proper evaporation of their moisture, and on the other hand to maintain a suitable temperature of the asphalt composition during and after the mixing.
The asphalt composition is then kept at an elevated temperature during transportation to the site of use and until it is laid down as a layer on the ground to secure suitable workability of it, and is then compacted before cooling down to ambient temperatures. Once the compacted layer has cooled down, the surface is ready to use.
The use of elevated temperatures in the mixing, transportation, lay-down and compacting steps is energy consuming and causes fume emissions of volatile hydrocarbons from the bituminous binder.
There is thus a need for reducing the temperature in the aggregate-mixing, transportation, lay down and compaction steps, while at the same time achieving the desired air void content and density of the finished paved surface.
This may be achieved by adding one or more additives to the bitumen, which results in a bituminous binder with a maintained workability at a lower temperature compared to the bitumen without such additives. Such additives have been referred to as warm-mix additives, as they allow a lowering of the various process temperatures from what is referred to in the industry as “hot” to what is referred to in the industry as “warm”.
Lowering the process temperatures by adding such warm-mix additives would reduce the energy consumption, would allow for longer haul distances, as the mix, at a lower temperature will maintain a workable rheology when it reaches the construction site, thereby extending the paving season, as it may allow paving to be performed at lower ambient temperatures. Lower processing temperatures may also reduce oxidative hardening of the bitumen, thereby extending the pavement life.
Several processes and products are being introduced into the market to reduce compaction and mixing temperatures.
For instance, EP 2 166 039 A1 to Ceca S. A. relates to methods for the production of asphalt mixtures by using a bituminous composition that has been stored for a given period of time and which composition comprises at least one bitumen and at least one additive that allows asphalt mixture production at reduced temperatures.
However, moisture damage of the pavement is of great concern, and can occur by two major pathways. First, water will displace the bituminous binder from the aggregate surface, especially the ones containing higher amounts of silica, as water has a higher affinity for the aggregate surface compared to the bitumen, and as there is a lack of chemical bonding of bitumen to the aggregate surface. This deleterious process is known as stripping. Secondly, water, over a period of time and under a repeated load can get inside the bitumen and reduce the cohesive strength of the bituminous binder.
Further, the use of the prior art warm-mix additives in the bitumen typically causes a loss of the stiffness modulus of the eventual pavement.
There is still a need in the art to provide additives that on the one hand lowers the temperatures at which the bituminous binder and the asphalt composition can be processed, and that on the other hand provides improved anti-stripping properties, reduces the loss of cohesive strength, and reduces the loss of stiffness modulus commonly associated with such additives.